In the American Harvest cookbook, Chef Sonnenschmidt notes that he likes to "make Braised Short Ribs on a cold day...letting it braise and perfume the air for much of the day. If time permits, and you can resist digging in immediately, cover, refrigerate, and skim off the surface fat the next day." Why is stock a key component of this flavorful dish? And why might you need to skim surface fat off of the dish the next day